THREE DIMENSIONAL PRINTING MATERIAL SYSTEM
AND METHOD USING PEROXIDE CURE
Related Application
[0001] This application claims priority to U.S. Provisional Patent Application Serial No.
60/873,730, filed December 8, 2006, the disclosure of which is hereby incorporated by
reference in its entirety.
Technical Field
[0002] This invention relates generally to rapid prototyping techniques and, more
particularly, to a three-dimensional printing material and method using a peroxide cure.
Background
[0003] The field of rapid prototyping involves the production of prototype articles and
small quantities of functional parts, as well as structural ceramics and ceramic shell molds for
metal casting, directly from computer-generated design data.
[0004] Two well-known methods for rapid prototyping include a selective laser sintering
process and a liquid binder Three Dimensional Printing process. These techniques are similar,
to the extent that they both use layering techniques to build three-dimensional articles. Both
methods form successive thin cross-sections of the desired article. The individual cross-
sections are formed by bonding together adjacent grains of a granular, (i.e., particulate)
material on a generally planar surface of a bed of the granular material. Each layer is bonded to
a previously formed layer at the same time as the grains of each layer are bonded together to
form the desired three-dimensional article. The laser-sintering and liquid binder techniques are
advantageous because they create parts directly from computer-generated design data and can
produce parts having complex geometries. Moreover, Three Dimensional Printing may be
quicker and less expensive than machining of prototype parts or production of cast or molded
parts by conventional "hard" or "soft" tooling techniques that can take from a few weeks to
several months, depending on the complexity of the item.

[0005] An early Three Dimensional.Printing technique, described.in U.S. Patent No.
5,204,055, incorporated herein by reference in its entirety, describes the use of an ink-jet style
printing head to deliver a liquid or colloidal binder material to sequentially applied layers of
powdered material. The three-dimensional ink-jet printing technique or liquid binder method
involves applying a layer of a powdered material to a surface using a counter-roller. After the
powdered material is applied to the surface, the ink-jet printhead delivers a liquid binder in a
predetermined pattern to the layer of powder. The binder infiltrates into gaps in the powder
material and hardens to bond the powder material into a solidified layer. The hardened binder
also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the
previous steps are repeated, building successive cross-sectional portions until the final article is
formed. Optionally, an adhesive may be suspended in a carrier that evaporates, leaving the
hardened adhesive behind. The powdered material may be ceramic, plastic or a composite
material. The liquid binder material may be organic or inorganic. Typical organic binder
materials used are polymeric resins or ceramic precursors, such as polycarbosilazane.
Inorganic binders are used where the binder is incorporated into the final artieles; silica is
typically used in such an application.
[0006] Some groups, e.g., Fuji, have performed ultraviolet cure of acrylate binders over
particulate material. Acrylate binders provide several advantages. First of all, they are curable
by ultraviolet (UV) light, thereby enabling a faster forming process then is possible with other
typical curing methods. Secondly, they allow the formation of articles having surfaces with
plastic appearances, thereby enabling more realistic modeling of various objects. Finally,
because acrylate binders are essentially solids, no evaporation takes place after the binders are
printed, thereby allowing the formation of stable, tough structures.
[0007] The fast curing mechanism of UV initiation of (meth)acrylate polymerization may
cause excessive distortion in free flowing particulate material, resulting in curling of the printed
part, which may make the printing of parts having a thickness greater than 1 millimeter
exceedingly difficult. To reduce curling due to fast curing, a first printed layer may be formed
on a glass build plate, adhering thereto.

Summary of the Invention
[0008] In an embodiment of the invention, strong parts may be made by Three
Dimensional Printing over particulate material build material without a need for infiltration.
Typical existing printing processes include a post-processing infiltration step to increase the
strength of the printed article. Articles printed with the peroxide-containing binders described
herein have strengths comparable to that of infiltrated articles, e.g., about 20 MPa, thereby
eliminating a need for the infiltration step.
[0009] The fast curing mechanism of UV initiation of (meth)acrylate polymerization may
cause curling and distortions to occur immediately from shrinkage due to the instantaneous
decrease in free volume from the conversion of carbon-to-carbon double bonds of the
individual (meth)acrylate monomer to single carbon-to-carbon bonds to another (meth)acrylate
monomer. This may hinder the production of articles thicker than 1 mm from free-flowing
particulate build materials, as articles tend to be destroyed in the process. The slower curing
mechanism of the peroxide initiation according to the invention slows down the rate of carbon-
to-carbon double bond conversion into single bonds and thus reduces the immediate curling
and distortion. Moreover, the acrylate-containing binder cures upon contact with the
particulate material, thus providing the advantage of a stable two-component product.
[0010] Both aerobic curing and anaerobic curing may be employed in embodiments of the
invention. In contrast to existing processes where amines may be used as oxygen scavengers
solely in ultraviolet curing, allyl ethers, as described herein, may be employed as oxygen
scavengers in both ultraviolet curing and peroxide initiation.
[0011] In an embodiment, the invention features a powder material system for Three
Dimensional Printing including a substantially dry particulate material that includes an
insoluble filler, a soluble filler, and a transition metal catalyst. The dry particulate material is
suitable for use in Three Dimensional Printing to form an article having a plurality of layers, the
layers including a reaction product of the particulate material and a non-aqueous fluid that contacts
the particulate material during Three Dimensional Printing.
[0012] One or more of the following features may be included. The particulate material may
possess an internal angle of friction greater than 40° and less than 70°. The particulate material
possess a critical surface tension greater than 20 dynes/cm. The particulate material may
include about 50% - 90% by weight of the insoluble filler, about 10 - 50% by weight of the
soluble filler, and about 0.01 - 0.5 % by weight of the transition metal catalyst.

10013] The insoluble filler may include or consistessentially of solid glass microspheres,
hollow glass microspheres, solid ceramic microspheres, hollow ceramic microspheres, potato
starch, tabular alumina, calcium sulfate hemihydrate, calcium sulfate dihydrate, calcium
carbonate, ultra-high molecular weight polyethylene, polyamide, poly-cyclic-olefins,
polyurethane, polypropylene and combinations thereof.
[0014] The soluble filler may include or consist essentially of methyl methacrylate
polymers, ethyl methacrylate polymers, butyl methacrylate polymers, polyvinylbutyral, and
combinations thereof. The soluble filler may have a molecular weight between 100,000 g/mol
and 500,000 g/mol.
[0015] The transition metal catalyst may include or consist essentially of cobalt (II)
octoate, cobalt (II) naphthenate, vanadium (II) octoate, manganese naphthenate and
combinations thereof.
[0016] The particulate material may include a pigment, e.g., about 0.5 to 5% by weight.
The pigment may include or consist essentially of zinc oxide, zinc sulfide, barium sulfate,
titanium dioxide, zirconium silicate, lead carbonate, and hollow borosilicate glass spheres.
[0017] The particulate material may include a processing aid, e.g., about 0.01 - 2.0 % by
weight of the processing aid. The processing aid may include or consist essentially of mineral
oil, propylene glycol di(caprylate/caprate), petroleum jelly, propylene glycol, di-isobutyl
phthalate, di-isononyl phthalate, polyalkyleneoxide modified heptamethyltrisiloxanes,
polyalkyleneoxide modified polydimethylsiloxanes, secondary ethoxylated alcohols,
fluorinated hydrocarbons, saturated hydrocarbon resin tackifiers, and combinations thereof.
[0018] In another aspect, the invention features a kit including a substantially dry
particulate material including an insoluble filler, a soluble filler, and a transition metal catalyst.
The kit also includes a fluid binder including a (meth)acrylate monomer, an allyl ether
functional monomer and/or oligomer, and organic hydroperoxide.
[0019] One or more of the following features may be included. The fluid binder may have
a contact angle of less than 25° on the particulate material. The fluid binder may include about
40% - 95% by weight of the (meth)acrylate monomer, about 5 - 25% by weight of the allyl
ether functional monomer/oligomer, and about 0.5 - 5% by weight of the organic
hydroperoxide. The fluid binder may also include 0 - 1% by weight of surfactant. The fluid
binder may include a (meth)acrylate oligomer, e.g., about 10 - 40% by weight of the

(meth)acrylate oligomer. The fluid binder may include a first accelerator, e.g., up to about 2%
by weight of the first accelerator. The first accelerator may include dimethylacetoacetamide.
[0020] A 1 mm penetration hardening rate of the substantially dry particulate material upon
application of the fluid binder is selected from a range of 0.01/min to 1.0 /min. The dry
particulate material may include a pigment and/or a processing aid.
[0021] In yet another aspect, a method for forming an article by Three Dimensional
Printing includes the step of providing a substantially dry particulate material including a
plurality of adjacent particles, the particulate material comprising a transition metal catalyst. A
fluid binder is applied to at least some of the plurality of particles in an amount sufficient to
bond mose particles together to define at least a portion of the article, the fluid binder including
a (meth)acrylate monomer, a (meth)acrylate oligomer, an allyl ether functional monomer
and/or oligomer, and organic hydroperoxide.
[0022] One or more of the following features may be included. The transition metal
catalyst may induce decomposition of the organic hydroperoxide to generate free radicals and
the free radicals initiate anaerobic polymerization of the (meth)acrylate monomer and oligomer;
and aerobic polymerization of the allyl ether functional monomer/oligomer.
[0023] The fluid binder may include a first accelerator. The particulate material may
include an insoluble filler, a soluble filler, a pigment, and/or a processing aid.
Brief Description of the Figures
[0024] The following drawings are not necessarily to scale, emphasis instead being placed
generally upon illustrating the principles of the invention. The foregoing and other features and
advantages of the present invention, as well as the invention itself, will be more fully
understood from the following description of exemplary and preferred embodiments, when read
together with the accompanying drawings, in which:
Figure 1 is a schematic view of afirst layer of a mixture of particulate material of an
embodiment of the invention deposited onto a movable surface of a container on which an
article is to be built, before any fluid has been delivered;
Figure 2 is a schematic view of an ink-jet nozzle delivering a fluid to a portion of the
layer of particulate material of Figure 1 in a predetermined pattern;

Figure 3 is a schematic view of a final article of an embodiment of the invention
enclosed in the container, the article made by a series of steps illustrated in Figure 2 and
embedded in the loose unactivated particles;
Figure 4 is a schematic view of the final article of Figure 3;
Figure 5 is a graph illustrating a typical response from the Washburn infiltration method
to determine the material constant and contact angle of a fluid against a particulate material;
Figure 6a is a magnified image of the particulate material consisting primarily of glass
microspheres and a soluble filler as the secondary component;
Figure 6b is a magnified image of the particulate material consisting of a 50/50 blend by
bulk volume of glass microspheres and calcium sulfate hemihydrates with a soluble filler as the
third component;
Figure 7 is a plot of flexural strength and flexural distance at break of particulate
materials using soluble fillers with varying molecular weights.
Figure 8 is a Zisman plot of a particulate material using a mineral oil processing aid;
Figure 9 is a Zisman plot of a particulate material using a combination of mineral oil
and a secondary ethoxylated alcohol surfactant as a processing aid;
Figures 10a and 10b are laser profilometer images comparing the effect of proper and
poor binder wetting on the bottom surfaces of articles;
Figure 11 is a Zisman plot of a particulate material using a combination of a saturated
hydrocarbon resin and mineral oil as a processing aid;
Figure 12 is a graph illustrating a hardness development response of a particulate
material and a fluid binder;
Figure 13 is the transformed plot of Figure 11, plotting the natural logarithm of the
force measured against time;
Figure 14 is a diagram illustrating the aerobic cure response time of thin-walled articles;
Figure 15 is a schematic diagram of a test part used to determine aerobic cure response;
Figure 16 is a graph illustrating the internal friction angle of various powders;
Figures 17a and 17b are laser profilometer images comparing the effect of particulate
materials with high internal angle of friction on finished article properties;
Figure 17c is a CAD drawing of the par portion printed in Figures 17a and 17b;

Figure 18a and 18b are laser profllometer images comparing the.effect of particulate
material with low internal angle of friction on finished article properties; and
Figure 18c is a CAD drawing of the part portion printed in Figures 18a and 18b. .
Detailed Description
Three Dimensional Printing
[0025] Referring to Figure 1, in accordance with a printing method using the materials
system of the present invention, a layer or film of a particulate material 20, i.e., an essentially
dry, and free-flowing powder, is applied on a linearly movable surface 22 of a container 24.
The layer or film of particulate material 20 may be formed in any suitable manner, for example
using a counter-roller. The particulate material 20 applied to the surface includes an insoluble
filler material, a soluble filler material, and a transition metal catalyst. The particulate material
20 may also include a pigment and/or a processing aid material.
[0026] Referring to Figure 2, an ink-jet style nozzle 28 delivers a fluid binder 26 to at least
a portion 30 of the layer or film of the particulate mixture 20 in a two-dimensional pattern. The
fluid binder 26 delivered to the particulate material 20 includes a (meth)acrylate functional
monomer, an allylic functional monomer/oligomer, and an organic hydroperoxide. The fluid
binder 26 may also include a surfactant, an accelerator, and/or a (meth)acrylate functional
oligomer. According to the printing method, the fluid binder 26 is delivered to the layer or film
of particulate material 20 in any predetermined two-dimensional pattern (circular, in the
figures, for purposes of illustration only), using any convenient mechanism, such as a drop-on-
demand (DOD) printhead driven by software in accordance with article model data from a
computer-assisted-design (CAD) system.
[0027] The first portion 30 of the particulate material activates the fluid binder 26, causing
the fluid binder to initiate polymerization into a solid that adheres together the particulate
mixture to form a conglomerate of the particulate material 20 (powder) and fluid binder 26.
The conglomerate defines an essentially solid circular layer that becomes a cross-sectional
portion of an intermediate article 38 (see, e.g., Figures 3 and 4). As used herein, "activates" is
meant to define a change in state in the fluid binder 26 from essentially stable to reactive. This
definition encompasses the decomposition of the organic hydroperoxide in the fluid binder 26
once in contact with the transition metal in the particulate material 20. When the fluid initially

comes into contact with the particulate mixture, it immediately flows outwardly (on a
microscopic scale) from the point of impact by capillary suction, dissolving the soluble filler
within a time period, such as 30 seconds to one minute. A typical droplet of fluid binder has a
volume of about 50 picoliters (pi), and spreads to a diameter of about 100 micrometer (urn)
after coming into contact with the particulate mixture. As the fluid binder dissolves the soluble
filler, the fluid viscosity increases dramatically, arresting further migration of the fluid from the
initial point of impact. Within a few minutes, the fluid with soluble filler dissolved therein
flows and adheres to the insoluble filler, forming adhesive bonds between the insoluble filler
particulate material. The fluid binder is capable of bonding together an amount of the
particulate mixture that is several times the mass of a droplet of the fluid. As the reactive
monomers/oligomer of the fluid binder polymerize, the adhesive bonds harden, joining the
insoluble filler particulate material and, optionally, pigment into a rigid structure, which
becomes a cross-sectional portion of the final article 40.
(0028] Any dry particulate mixture 32 that was not exposed to the fluid remains loose and
free-flowing on the movable surface 22. The dry particulate mixture is typically left in place
until formation of the intermediate article 38 is complete. Leaving the dry, loose particulate
mixture in place ensures that the intermediate article 38 is fully supported during processing,
allowing features such as overhangs, undercuts, and cavities to be defined and formed without
the need to use supplemental support structures. After formation of the first cross-sectional
portion of the intermediate article 38, the movable surface 22 is indexed downwardly, in an
embodiment, and the process is repeated.
(0029] Using, for example, a counter-rolling mechanism, a second film or layer of the
particulate mixture is then applied over the first layer, covering both the rigid first cross-
sectional portion, and any proximate loose particulate mixture. A second application of fluid
binder follows in the manner described above, dissolving the soluble filler and forming
adhesive bonds between at least a portion of the previous cross-sectional formed portion, the
insoluble filler particulate material, and, optionally, pigment of the second layer, and hardening
to form a second rigid cross-sectional portion added to the first rigid cross-sectional portion of
the final article. The movable surface 22 is again indexed downward.
(0030] The previous steps of applying a layer of particulate mixture, including the soluble
filler, applying the fluid binder, and indexing the movable surface 22 downward are repeated
until the intermediate article 38 is completed. Referring to Figure 3, the intermediate article 38

may be any shape, such as cylindrical. At the end of the process, only a top surface 34 of the
intermediate article 38 is visible in the container 24. The intermediate article 38 is typically
completely immersed in a surrounding bed 36 of dry and loose particulate material.
Alternatively, an article could be formed in layers upward from an immovable platform, by
successively depositing, smoothing, and printing a series of such layers.
[0031] Referring to Figure 4, the dry and loose particulate material may be removed from
the intermediate article 38 by pressurized air flow or a vacuum. After removal of the dry and
loose particulate material from the intermediate article 38, a post-processing treatment may be
performed, such as heating in an oven, painting, etc. to define a final article 40, having the
same shape as intermediate article 38, but with additional desired characteristics, such as a
smooth surface appearance, neutral chroma, high lightness, toughness, strength, and flexibility.
Particulate material
[0032] One preferred embodiment of a particulate material suitable for Three Dimensional
Printing, i.e., a substantially dry particulate material, includes or consists essentially of:
insoluble filler 50 - 90 wt%
soluble filler 10 - 50 wt%
pigment 0.0-5 wt%
transition metal catalyst 0.01 - 1 wt%
processing aids 0.01-2.0 wt%
[0033] A preferred particle size, i.e., diameter, of components of the particulate material is
less than about 125 microns and greater than about 30 microns.
[0034] The insoluble filler provides dimensional stability and adhesion for strength of an
article formed from the particulate material. One suitable insoluble filler for use with
embodiments of the invention is glass microspheres. The glass microspheres may be made
from borosilicate glass with an index of refraction of 1.5 and may be spherical with a particle
size distribution ranging from greater than about 20 microns to less than about 125 microns,
more preferably between 40 and 90 microns. The glass microspheres may be treated with an
amino-silane so that the microsphere surface may have an amine functionality and provide
better adhesion to a (meth)acrylate based binder. An example of such glass spheres is
SPHERIGLASS 2530 CP03, available from PQ Corporation based in Valley Forge, PA. This
supplier also offers another glass microsphere product, T-4 SIGN BEADS, having an index of

refraction of 1.9 that offers better light scattering to create a more neutral and lighter color than
that of SPHERIGLASS 2530 CP03. Another suitable borosilicate glass bead product with an
index of refraction of 1.5, but more translucent than Spheriglass 2530 CP03, is GL0179 from
Mo-Sci Specialty products, LLC based in Rolla, MO. The clearer product imparts a more
neutral color to articles than both the SPHERIGLASS and T-4 SIGN BEAD products, which
may be desirable for attaining a wider color gamut.
[003S] Various types of insoluble fillers suitable for use with embodiments of the invention
include solid glass spheres, hollow glass spheres, solid ceramic spheres, hollow ceramic
spheres, potato starch, tabular alumina, calcium sulfate hemihydrate, calcium sulfate dehydrate,
calcium carbonate, ultra-high molecular weight polyethylene, polyamide, poly-cyclic-olefins,
polyurethane, polypropylene, and combinations thereof.
[0036] It may be preferable that the insoluble filler consist mostly of spherical shaped
particles with a particle size distribution with 10% less than 30 to 40 microns, with 90% less
than 90 to 125 microns, with 50% between 50 to 70 microns. Angular, non-spheroid shaped
particles with wide particle size distributions with 10% less than 3 to 30 microns, with 90% less
than 60 to 90 microns, and with 50% of the particles between 20 to 60 microns are to be
avoided or used less than 10% by weight in the particulate material in order to provide low
capillary pressure which in turn lowers the amount of distortion. The addition of angular
shaped particles may decrease the average capillary radius of the particulate material thus
increasing capillary pressure and increasing distortion of the final article.
[0037] Capillary pressure may be described by Equation 1 below, which is derived into a
simple form from the equation of Young and Laplace:

where Ap is the capillary pressure, which is the pressure difference across the fluid interface, yiv
is the surface tension at the liquid-vapor interface of the fluid, r is the average radius of the
capillaries, and 0 is the contact angle at the fluid-solid interface.
[0038] The contact angle, 0, is the angle of contact between a liquid and solid. A contact
angle of 0° suggest that the fluid will spontaneously wet the entire surface of the solid to which
it is applied, while a contact angle greater than 90° suggests that the fluid will not
spontaneously spread and wet the surface of the solid to which it is applied. Spontaneously

used herein is in reference to thermodynamic equilibrium, and does not denote an instance of
time. The contact angle may be defined by the Young and Dupre equation:

where y„ is the surface energy at the solid and vapor interface, and is the surface energy at
the solid and liquid interface. The difference of in the numerator of Equation 2 may be
defined as the adhesion tension of the solid at the solid-liquid-vapor interfaces. It may be
desirable to have this adhesion tension greater than or equal to the surface tension of the fluid at
the liquid-vapor interface. The adhesion tension may be related to the surface characteristic
defined as the critical surface tension by Zisman, which is described in the following
paragraphs.
[0039 J One can see from Equation 1 that capillary pressure increases if the average radius
of the capillaries decreases and/or if the contact angle increases through an increase of the
fluid's surface tension, and/or the adhesion tension of the solid decreases. This effect of
capillary pressure infiltrating a porous medium may be measured by the Washburn infiltration
method. The Washburn equation describes the time a fluid takes to infiltrate into and through
porous medium. The Washburn equation is often used in the following form:

where 0is the contact angle at the liquid-solid interface, m is the mass of fluid, t is time, r\ is
the viscosity of the fluid, p is the density of the fluid, and c is a material constant.
[0040] The material constant c may be determined by infiltrating a porous medium with a
very low surface tension fluid that will have a contact angle of 0° against the solid surface of
particles comprising the porous medium. n-Hexane is a common fluid used for such purposes,
having a surface tension of 18 dynes/cm; it is assumed to have a contact angle of 0° against
most solid surfaces. This makes the value of cos# equal to 1 in Equation 3, thereby making it
possible to solve for the material constant c since the fluid properties of n-hexane are known.
This leaves one to measure the rate of mass increase of the fluid infiltrating the porous medium
over time. This mass-time response may be measured by use of a Kriiss Processor Tensiometer

K100 with accessories for Washburn contact angle measurement, available from KRUSS USA
based in Mathews, NC, or by use of a KSV Sigma 70 Tensiometer from KSV Instruments USA'
based in Monroe, CT. With these instruments, a vial of powder is prepared. The vial is
perforated at a bottom portion, with a piece of porous filter paper preventing the powder from
pouring through the perforated bottom. The vial filled with powder is attached to a
microbalance, and the bottom of the vial is brought into contact to the surface of the fluid, in
this case n-hexane. Software records the mass increase of the vial over time from the
microbalance as the fluid is drawn into the powder in the vial largely by capillary pressure.
One may then plot the mass squared over time, which should result in a straight line during the
time fluid is infiltrating into the powder in the vial (see Figure 5, that illustrates a typical
response from the Washburn infiltration method to determine the material constant and contact
angle of a fluid against a particulate material). The slope may be calculated from that plot,
which corresponds to the value of — in Equation 3. After the slope is calculated, one may
solve for the material constant c.
(0041] The material constant c is sensitive to the packing density of the powder in the vial
in which it is prepared, so it is preferable to use a method that consistently provides the same
packing density in the vial for each test. It is theorized that the material constant has the
following relationship:

where r is the average capillary radius of the porous medium, and n is the number of capillary
channels. Loosely packed powder will have a larger average capillary radius increasing the
material constant, and, conversely, densely packed powder will have smaller average capillary
radius decreasing the material constant.
[0042] The Washburn method described above was used to determine the material constant
of (i) a particulate material primarily composed of glass microspheres with a particle size
distribution in which 10% of the particles have a particle size, i.e., diameter, of less than 50
microns, 50% are less than 70 microns, and 90% are less than 100 microns and (ii) a particulate
material primarily composed of glass microspheres with calcium sulfate hemihydrate which is
an angular, non-spheroid shape particle with a particle size distribution in which 10% of the

{0043] Referring to Table 1, a comparison of material constants shows a significant
difference between the two particulate formulations. The particulate material consisting
primarily of glass microspheres exhibits a material constant almost six times greater than the
particulate material formulation consisting of the 50/50 blend by bulk volume of glass
microspheres and calcium sulfate hemihydrates. This difference suggests that the angular
grains of the calcium sulfate hemihydrate impart a denser packed particulate material that leads
to much smaller average capillary radii. The larger material constant of the particulate material
consisting primarily of glass microspheres suggest a larger average capillary radius, allowing
for a lower capillary pressure and thus would exhibit lower distortions on printed articles.
[0044] Referring to Figures 6a and 6b, magnified images taken from an Olympus SZX12
microscope of both particulate material formulations illustrate the particle distribution of the
two materials. Figure 6a is a magnified image of the particulate material consisting primarily
of glass microspheres and a soluble filler as the secondary component. Figure 6b is a
magnified image of the particulate material consisting of a 50/50 blend by bulk volume of glass
microspheres and calcium sulfate hemihydrates with a soluble filler as the third component.
[0045] The Washburn method may also be utilized to determine the contact angle the fluid
binder forms with the particulate material, since the material constant is can be determined for
each particulate formulation. The fluid binder formulation of Table 2 was used to determine
the contact angle the fluid has with each of the above particulate formulations of Table 1:


[0046] The contact angles given in Table 3 were determined using the fluid binder of Table
2 to infiltrate each of the particulate material samples in a vial.

[0047] The fluid binder wets the particulate material consisting primarily of glass
microspheres better than the formulation containing calcium sulfate hemihydrate because it
exhibits a contact angle of zero with the former. Articles printed from the particulate material
consisting of calcium sulfate hemihydrate along with glass microspheres exhibit distortions
such as the cupping of flat rectangular articles as capillary forces pull particles inward in the
printed area where fluid binder is applied. Articles printed from particulate material
formulations consisting primarily of glass microspheres between 70-90% by weight, or 50-75%
by bulk volume have consistently resulted in articles with very little to no distortion from
capillary forces.
[0048] The concepts presented here regarding contact angle, capillary pressure, and
adhesion tension may be found in the Physical Chemistry of Surfaces. Adamson, Arthur W.,
Interscience Publishers, Inc., 1967, and regarding the Washburn method in "Wettability Studies
for Porous Solids Including Powders and Fibrous Materials - Technical Note #302" by
Rulison, Christopher, 1996, which is a manufacturer's application note from KRUSS USA, the
disclosures of which are incorporated herein by reference in their entireties.
[0049] The soluble filler primarily helps to control the migration of binder through die
particulate material, which controls bleed or pooling of fluid binder in selectively printed areas,
and also provides extra strength and toughness to the final cured article. The soluble filler
helps control binder migration of binder by dissolving into the fluid binder deposited in the
selective areas to increase the viscosity of the fluid binder that decreases the rate of binder
migration. Soluble fillers suitable for use with embodiments of the invention include methyl

methacrylate polymers, ethyl methacrylate polymers, butyl methacrylate polymers,
polyvinylbutyral, and combinations thereof.
[0050] More specifically, a suitable soluble filler is a solid methacrylate polymer with a
glass transition temperature between about 40 and about 60 degrees Celsius and a molecular
weight from a range of about 100,000 to about 500,000 g/mol. Another example of a suitable
soluble filler is a polymethylmethacrylate/ethyl methacrylate co-polymer resin such as
ELVAC1TE 2014, available from Lucite International based in Cordova, TN. Another suitable
resin is a butylmethacrylate/methylmethacrylate copolymer resin such as NEOCRYL B-723,
available from NeoResins based in Wilmington, MA. The soluble filler may be processed to
achieve a particle size distribution where 10% of the particles are less than 20 to 30 microns,
and 90% of the particles are less than 80 to 100 microns, and 50% of the particles are between
50 and 70 microns. In some embodiments, the particulate material may be non-reactive such
that it does not swell or dissolve in the fluid binder.
[0051] The effect of a molecular weight of the soluble filler may be measured with a
Texture Analyzer TA-XT2i from Stable Micro System based in the United Kingdom. This
instrument may be used to measure a three-point flexural strength of a bar 5 mm thick, 5.7 mm
wide, and 50 mm long created from the application of fluid binder onto the particulate material
on a three-dimensional printer, supported on a two-point span spaced at a distance of 40 mm.
The force to break the test part with the force applied at the center of the 40 mm span may be
used to calculate an estimate of flexural strength. The distance to break the test part is also
recorded which may estimate the amount of strain the bar endures. Higher flexural distances at
break, as the strength increase, may relate to increased toughness of the article. This test was
performed on particulate material formulations using soluble fillers with varying molecular
weights listed in Table 4 using the fluid binder composition listed in Table 5.

[00S2] The flexural test bars were printed on a Spectrum Z®510 Three Dimensional Printer
available from Z Corporation in Burlington, MA modified to use a SM-128 piezoelectric jetting
assembly along with an Apollo II Printhead Support Kit both available from FUJIFILM
Dimatix based in Santa Clara, CA. The flexural test bars were printed applying the fluid binder
listed on Table 5 through the SM-128 jetting assembly over the particulate material at a layer
thickness of 100 microns. The fluid was deposited selectively and uniformly at each layer to
occupy 32% by volume of the flexural test part. The flexural test parts were allowed to solidify
for 1 hour before they were extracted from the build bed of the Spectrum Z510 and placed in a
60°C oven for 12 hours to cure. Table 6 summarizes flexural properties of the particulate
material compositions that were measured. Referring to Figure 7, a graphical representation of
the results collected is provided. The results suggest that soluble fillers with molecular weights
less than 100,000 g/mol exhibit lower flexural properties than soluble fillers with molecular
weights greater than 100,000 g/mol.


[0053] Inclusion of pigments may be used to impart a neutral color to provide a greater
color gamut and a high brightness to make white-looking articles. Preferably, the particulate
material may include pigments in a concentration of 0.5 - 5% by weight. Titanium dioxide is a
pigment with a refractive index of 2.4 that may be used, but its listing as a possible I ARC
carcinogen makes it undesirable for use in an office environment. Zinc oxide is an alternative
pigment with a refractive index of 2.0, and it is not listed as a carcinogen. Zinc oxide, available
from Sigma-Aldrich based in Milwaukee, WI, imparts the most neutral color over titanium
dioxide. Other suitable pigments include zinc sulfide, barium sulfate, zirconium silicate, lead
carbonate, and hollow borosilicate glass spheres.
[0054] Pigments may also be incorporated and bound into the insoluble filler or soluble
filler, which may be advantageous to prevent the particulate material from exhibiting excessive
dust and to agglomerate as the unbound pigments may adhere to the processing aids used to
control the desired spreading characteristics, causing the particulate formulation to lose its
desired flowability characteristics. OMNICOLOR UN0005 from Clariant based in Charlotte,
NC, is white colorant compound of pigment and a resin for injection molded plastics which can
be use as an alternative pigment source where the pigment is bound in the resin, reducing the
dustiness and maintaining the desired flowability characteristics while providing color. This
colorant and other types of colorant commonly used in injection molding applications may also
be used to color the soluble filler, such as ELVACITE 2014, through melt processing to make a
more uniform colored particulate formulation. DECOSOFT and DECOSILK are pigmented
polyurethane and acrylic microbeads respectively from Microchem based in Erlenback,
Switzerland commonly used to make colored or transparent, low gloss, soft-feel coatings.
These products may be used as an insoluble filler to impart tougher material properties while
imparting the desired color because of the pigment incorporated into the microbead product,
thus decreasing the dust and maintaining the desired flowability characteristics.
[0055] The transition metal catalyst may induce the decomposition of the organic
hydroperoxide in the fluid binder to generate free radicals and to catalyze the absorption of
oxygen for allyllic polymerization. Transition metals are metal ions that have multiple
oxidation states and can readily lose or gain electrons in the presence of oxidizing or reducing
agents, respectively. Metal catalysts based on copper, iron, vanadium, manganese titanium,
and cobalt are preferred, although other metal catalysts may be used. In particular, one suitable
transition metal catalyst includes cobalt (II) octoate in 65% mineral spirits from Sigma-Aldrich

based in St. Louis, Missouri. Other suitable metal catalysts include, e.g., cobalt (II)
naphthenate, vanadium (II) octoate, manganese naphthenate, and combinations thereof.
(0056] Processing aids may be used to affect particulate material spreading characteristics
to achieve a desirable internal angle of friction (see discussion below) and to reduce capillary
forces between the particulate material in contact with the fluid binder. Processing aids can
further assist in reducing nuisance dust of the particulate material. Mineral oil is a typical
processing aid that affects the flowability of the particulate material; it may be used from
0.01% to 1% by weight in the particulate formulation. The particulate material remains
substantially dry upon the inclusion of this small amount of mineral oil. Mineral oil, e.g., from
Sigma-Aldrich, may provide a good balance of particulate cohesion and low plasticizing of the
soluble filler without reducing capillary pressure. Hydrogenated hydrocarbon resins, such as
REGALREZ 1094 from Eastman based in Kingsport, TN, are tackifiers that may be used as
processing aid to increase the viscosity of the mineral oil and may be 0.01 to 2% by wt of the
particulate material. The hydrocarbon resin increases the viscosity of the processing aid that
imparts a unique cohesiveness and flowability characteristic, whereby the particulate material,
under shear from a counter-rolling spreader rod, becomes a free-flowing powder. The desired
cohesion is restored while at rest to resist dragging while successive layers are being spread.
The increase in viscosity assists in the fracture of the inter-particle adhesive necks of fluid that
the processing aids create to control flowability characteristics under shear; the adhesive necks
of fluid then slowly reform while the particulate material is at rest. The inter-particular
adhesive necks of fluid that lower viscosity processing aid imparts do not fracture as easily
under shear because the processing aids are allowed to flow more easily and faster to reform
the inter-particular adhesive necks of fluid.
[0057] Other processing aids suitable for use with embodiments of the invention include,
e.g., propylene glycol di(caprylate/caprate), petroleum jelly, propylene glycol, di-isobutyl
phthalate, di-isononyl phthalate, polyalkyleneoxide modified heptamethyltrisiloxanes,
polyalkyleneoxide modified polydimethylsiloxanes, secondary alcohol ethoxylates,
hydrogenated hydrocarbon resins, and combinations thereof.
[0058] A surfactant is a typical processing aid that may be used in conjunction with
mineral oil to reduce the capillary forces between the particulate material in contact with the
fluid binder by increasing the critical surface tension of the particulate material. Surfactants
may be used in a range of 0 to 1% by weight of the particulate material. Silicone surfactants,

such as SILWET L-7608 or COATOSIL L-77 from General Electric Company based in
Wilton, CT having a reported capability of reducing surface tension of water to less than 25
dynes/cm, may effectively reduce capillary forces between particles of the particulate material
in contact with the non-aqueous fluid binder. Secondary ethoxylated alcohols hydrocarbon
surfactants, such as TERGITOL 15-S-7 and TERGITOL-15-S-5 from DOW based in Midland,
MI, also may effectively reduce capillary forces between particles of the particulate material in
contact with the non-aqueous fluid binder.
[0059] The effect of the surfactant increasing the surface energy of the particulate material
may be measured using the Washburn method describe earlier by infiltrating a particulate
material formulation with a series of liquid solutions with varying surface tension values. The
contact angles, 8, are determined for each surface tension. Then the cos 6 values are plotted
against the surface tension values to construct a Zisman plot. The data are used to linearly
extrapolate a trend line to the value where cos 8 equals 1 (when 0= 0°) to determine the critical
surface tension of the particulate material which was described earlier to be related to the
adhesion tension of the solid at the solid-liquid-vapor interfaces. This test was performed on
the formulations listed in Table 7. See Figures 8 (particulate material with paraffinic oil
processing aid) and 9 (particulate material with a paraffinic oil and surfactant blend processing
aid).
[0060] Further discussion regarding critical surface tension may be found in Physical
Chemistry of Surfaces. Adamson, Arthur W., Interscience Publishers, Inc., 1967, and regarding
the Washburn method in "Wettability Studies for Porous Solids Including Powders and Fibrous
Materials - Technical Note #302" by Rulison, Christopher, 1996, which is a manufacturer's
application note from KRUSS USA; these disclosures are incorporated herein by reference in
their entireties.

Fluid binder
[0062] One preferred embodiment of a fluid binder suitable for Three Dimensional Printing
includes or consists essentially of:
(meth)acrylate monomer 40 - 90 wt%
(meth)acrylate oligomer 0-40 wt%
allyl ether functional monomer/oligomer 5-25 wt%
organic hydroperoxide 0.5 - 5 wt%
accelerator 0-2 wt%
surfactant 0-1 wt%
[0063] The (meth)acrylate (i.e., methacrylate and/or acrylate) monomers and oligomers
provide the properties of strength and flexibility. Such monomers and oligomers may be
procured from Sartomer based in Exton, PA.
[0064] The allyl ether monomer/oligomer provides the oxidative drying of the binder on the
surface of the article so that the surface is not tacky. Allyl ether monomers may be procured
from Perstorp based in Sweden. Suitable oligomers with allyl functionality may be obtained
from Sartomer, who offers CN-9101 urethane allyl functional oligomer. Bomar Specialty
Chemicals based in CT offers BXI-100, a poly-allyl-glycidyl-edier oligomer, another suitable
allyl functional oligomer.
[0065] The organic hydroperoxide is the free radical initiator for the anaerobic
polymerization of the (meth)acrylate monomers and oligomer, and the aerobic polymerization of
the allylic monomer/oligomer. A suitable organic hydroperoxide is curriene hydroperoxide
available as LUPEROX CU90 from Arkema based in Philadelphia, PA. The transition metal
catalyst induces the decomposition of the organic hydroperoxide, thus providing free radicals for
subsequent reactions and catalyzes the absorption of oxygen at the surface. Another organic
hydroperoxide suitable for use with some embodiments is tert-butyl hydroperoxide, is available
as T-HYDRO from Lyondell Chemical Company based in Houston Texas.
[0066] The surfactant is a preferred additive in the formulation of the fluid binders used in
Three Dimensional Printing to reduce the surface tension of the binder so that the surface tension
is equal to or less than the critical surface tension of the particulate material, such that the contact
angle of the fluid binder against the particulate material is less than 25°, but preferably closer to
if not equal to 0°. This allows the fluid binder to wet out onto the particulate material without
creating large capillary forces that may cause (i) fissuring at points where the printed area on the

particulate material splits apart and (ii) balling where the fluid binder sits on the surface of the
particulate material. Both of these occurrences may cause surface defects on the bottoms of flat
surfaces of printed articles.
[0067] Referring to Figures 10a and 10b, the effect of the fluid binder formulation is
illustrated by laser profilometer scans of flat bottom surfaces of articles at 50 micron resolution
on die x and y axes. Figure 10a illustrates an example of good wetting behavior with contact
angles less than 25° when the binder has a surface tension at or below a critical surface tension
of the particulate material and wets smoothly over the particulate material. For example, the
critical surface tension of the particulate material may be greater than 20 dynes/cm. Figure 10b
illustrates an example of poor wetting behavior with contact angles greater than 25° when the
binder has a surface tension greater than the critical surface tension of the particulate material
causing the binder to wet irregularly over the particulate material and creating fissures.
[0068] A suitable surfactant is a polyether modified acryl functional polydimethylsiloxane
surfactant available as BYK UV 3500 from BYK Chemie based in Hartford, CT. This surfactant
is a wetting agent commonly used in UV curable coatings to ensure a smooth finish on substrates
and, when used at 0.05% by weight in the fluid formulation, reduces the surface tension to about
25 +/- 1 dynes/cm. Other suitable surfactants may include fluorinated surfactants such as the
20NYL surfactants available from DuPont, which can reduce the surface tension of the fluid
binder down to 20 dynes/cm.
[0069] Fluid formulations of various embodiments of the instant invention are somewhat
similar to anaerobic adhesive formulations commonly known as "threadlockers" such as
LOCTITE 290 from Loctite based in Rocky Hill, CT and which is disclosed by Krieble in U.S.
Patent No. 2,895,950 assigned in 1957 to American Sealants Company based in Hartford, CT,
incorporated herein by reference in its entirety. Aerobically curing formulations using allyl
ethers are also known to the art, as described by Cantor et al. in U.S. Patent No. 5,703,138
assigned to Dymax Corporation, incorporated herein by reference in its entirety. FUJ1FILM
Dimatix based in Santa Clara, CA has a published application note describing the application of
LOCTITE 290 adhesive through one of their piezo jetting assemblies to accurately deliver
adhesive to a substrate. However, these formulations do not include a surfactant. The fluid
adhesive products described in these references do not have the proper surface tension
requirements needed for proper wetting, if they were applied onto the particulate material as
described in various embodiments of the instant invention. These materials are not intentionally

[0070] Referring to Table 11, the high contact angle LOCTITE 290 has on the particulate
material formulation indicates that this product would not wet out properly onto the particulate
material when applied during Three Dimensional Printing, and would create articles with rough,
irregular bottom surfaces, having defects similar to the defects illustrated in Figure 10b. A fluid
binder properly formulated to have a surface tension lowered to at least 25 dynes/cm so that it
has a contact angle less than 25° and close to, if not equal to 0° will wet out the powder properly,
resulting in a smooth bottom facing surface with less edge curling distortion, as is exhibited in
Figure 10a.
[0071} Surfactants may be used in photocurable inkjet fluid formulation, as disclosed, for
example, in U.S. Patent No. 6,433,038 to Tanabe, where surfactants are used to stabilize dyes
and pigments in the disclosed fluid inkjet formulation. Huo et al., in an international patent
application PCT/US2005/025074 disclose the use of surfactants to improve wettability of the
fluid over non-porous plastic substrates and to control the dynamic surface tension of the fluid
for faster meniscus reformation at the nozzle of a DOD device during jetting. These
formulations do not use surfactants to decrease the capillary pressure exerted by the fluid when
applied on a particulate material, as disclosed herein.
[0072] Another exemplary formulation listed on Table 12 shows a particulate powder
formulation with a lower critical surface tension than critical surface tensions of particulate
formulations disclosed on Table 7. See Figure 11, which is a Zisman plot of a particulate
material including a tackifier processing aid. The surface tension of the fluid binder is
essentially at the critical surface tension of the particulate material, and therefore results in a
contact angle equal to 0°. The contact angle may be greater than 0° and possibly less than 25° if
the critical surface tension is 2 dynes/cm less than the surface tension of the binder. This upper

limit of a contact angle is estimated from Equation 2 by. dividing the critical surface tension of
the solid by the surface tension of the fluid. The contact angle of the fluid binder against both of
the particular material listed in Table 12 was determined from the Washburn method to have an
average cos lvalue of 1.02 +/- 0.05 at 99% confidence, which would result in a contact angle
between 0° and 14° within the 99% confidence interval range of the cos 6 value. This fluid
binder, when applied to the particulate material disclosed in Table 12, results in proper wetting
of the fluid binder over the particulate material to impart a smooth bottom finish, as illustrated in
Figure 10a.

Kit
[0073] A kit may include various combinations of the substantially dry particulate material
and a fluid binder described above. For example, a kit may include (i) a substantially dry
particulate material comprising an insoluble filler, a soluble filler, and a transition metal catalyst,
and (ii) a fluid binder including a (meth)acrylate monomer, at least one of an allyl ether
functional monomer or an allyl ether functional oligomer, and an organic hydroperoxide.
[0074] The fluid binder may have a contact angle of less than 25° on the particulate material.
In an embodiment, the fluid binder may include about 40% - 95% by weight of the

(meth)acrylate monomer, about 5 - 25% by weight of the allyl ether functional
monomer/oligomer, and about 0.5 - 5% by weight of the organic hydroperoxide. The fluid
binder may also include 0% - 1% by weight of surfactant. The fluid binder may include a
(meth)acrylate oligomer, e.g., about 10 - 40% by weight of the (meth)acrylate oligomer. The
fluid binder may also include a first accelerator such as dimethylacetoacetamide, e.g., up to
about 2% by weight of the first accelerator.
[0075J A 1 mm penetration hardening rate of the substantially dry particulate material upon
application of the fluid binder may be e.g., 0.01/min to 1.0 /min. The dry particulate material
may include a pigment and/or a processing aid.
Printing method
[0076] An article may be defined by selectively printing the fluid binder over particulate
material. The fluid binder includes a (meth)acrylate monomer, a (meth)acrylate oligomer, an
allyl ether functional monomer and/or oligomer, and organic hydroperoxide and, optionally, a
first accelerator. The amount of binder deposited onto the particulate layer can range from 20%
to 35% of the volume of the selectively printed area at a predetermined layer thickness between
50 to 175 microns, and more preferably between 75 and 125 microns. The particulate material
includes a plurality of adjacent particles, comprising a transition metal catalyst and, at least one
of an insoluble filler, a soluble filler, a pigment, a second accelerator, and a processing aid. The
transition metal catalyst induces decomposition of the organic hydroperoxide to generate free
radicals. The free radicals initiate anaerobic polymerization of the (meth)acrylate monomer and
oligomer, and aerobic polymerization of the allyl ether functional monomer/oligomer.
[0077] The complete polymerization, i.e., cure, of the article may take between about 30
minutes and about 6 hours to complete after the formation of a solid article, after all the layers of
the article have been printed. In a conventional UV curing process, the curing happens
substantially instantaneously, so that the printed article may be removed from the printer as soon
as the printing is complete. Sano, in U.S. Patent Application Publication No. 2007/0007698 and
U.S. Patent 7,300,613, describes primarily the use of photocurable resins applied onto powder
via a drop-on-demand printhead as well as two component curing strategies such as epoxy-amine
thermosetting resins; Kramer, et al, in U.S. patent 7,120,512 assigned to Hewlett-Packard in
Houston, TX, also disclose the use of photocurable resins applied over powder using a drop-on-
demand printhead, as well as alternative embodiments of two component systems.

[0078] It was found-that photocurable fluid binders are generally not suitable for Three
Dimensional Printing because of the instantaneous curing leading to immediate shrinkage, which
leads to the first 2 to 10 layers of selectively printed areas to curl and warp out of the plane of the
build bed to be eventually dragged and displaced in or completely off the build bed. Sano
suggests the use of photocurable resins that polymerize via ring opening mechanism such as
epoxides and oxetanes to limit the degree of shrinkage. However, such mechanisms tend to be
sensitive to humidity and the alkalinity of the environment and substrate to which the resins are
applied.
[0079] Patel, et al., have international applications published through the World Intellectual
Property Organization (publication numbers WO 03/016030 and WO 02/064354 Al) with
Vantico as the assignee (now owned by Hunstman based in TX) that describe the use of various
embodiments of applying photocurable resins and two-component resins. Three Dimensional
Printing apparatuses and methods using ultraviolet cure are disclosed by Yamane, et al, in U.S.
Patent 5,149,548 assigned to Brother Kogyo Kabushiki Kaisha in Japan, which describes the use
of a two part curable resin utilizing microcapsules encapsulating a curing agent deposited with a
drop-on-demand printhead. The microcapsules are broken upon exposure to ultraviolet light.
[0080] Oriakhi, et al., in the TJ. S. Patent Application 2005/0093194 assigned to Hewlett-
Packard, discloses the use of a particulate material comprising primarily a polymeric filler and a
peroxide initiator, and a fluid binder comprising an activator for the peroxide initiator. This is
the reverse of the current embodiment, and also does not include an aerobic curing mechanism
for the surface of the article.
[0081] In embodiments of the current invention employing a peroxide cure process, a user
typically waits the above-indicated time after the article is printed before removing the article
from the printer. The article may be heated to a range of about 40°C to about 100°C to
accelerate the aerobic cure at the surface of the article. Heat may be supplied through
convection, conduction, infra-red radiation, microwave radiation, radio-wave radiation, or any
other suitable method.
[0082] The cure rate between a photocurable binder and the current embodiment may be
illustrated by comparing the hardening rate by measuring the force it takes to penetrate 1 mm.
into the surface of a mass mixture consisting of fluid binder and particulate material with a 0.5
inch spherical probe. Such a test of a 1 mm penetration hardening rate may be performed with a
Texture Analyzer TA-XT2i with a P/0.5S stainless steel spherical probe from Stable Micro

System based in the United Kingdom. The following particulate material system used in this test
is listed in Table 13.

[0083] The binder formulation used in this test is given in Table 14.

[0085] The hardness development was measured at 15 minute intervals using the spherical
probe to measure the force to penetrate 1 mm into the mixture contained in the polypropylene
dish. In the case of the photocurable example, the mixture in the polypropylene dish was
exposed to 30 seconds of ultraviolet light using a RC250B Flash Curing unit from XENON
Corporation based in Wilmington, MA. The hardness development of the photocurable example
is the plot of the penetration force at 30 seconds. Figure 12 shows the typical development
response collected, i.e., of particulate material A mixed with a fluid binder 1. The natural
logarithm of the force is taken to determine the hardening rate from the slope of the transformed
data before the force plateaus. Referring to Figure 13, a transformed plot of Figure 12 plots the
) natural logarithm of the force measured against time. The hardness development can be modeled
by the following equation:

where Fo is the initial penetration force that would be measured at time zero, m is the hardness
• rate, and t is the time. Table 16 lists hardness rates determined from the data collected.


[0086] One can see that the photocurable example exhibits a hardness development rate on
the order of 1000X greater than the current embodiment. This hardness rate is related to the rate
of conversion of double bonds on the (meth)acrylate monomer. The conversion of the carbon-to-
carbon double bonds into single carbon-to-carbon bonds with other monomers decreases the
amount of free volume in the fluid binder as it polymerizes. The instantaneous conversion of
monomers into a polymer in a photocurable fluid binder causes an instantaneous shrinkage upon
exposure to ultraviolet light, which forces selectively printed areas to curl and warp out of the
plane of the build bed, causing the selectively printed areas to be dragged and displaced as
successive layers are spread. The slower hardening rate of some embodiments relates to a
slower conversion rate and where selectively printed areas do not exhibit the immediate
distortion of curling and warping out of the plane of the build bed to successively print layer
upon layer without dragging or displacement of features on an article. Preferably, the 1 mm
penetration hardening rate is between 0.01/minute and 1.0/minute..
[0087] Strength development of the current embodiment can also be measured using the
earlier described Texture Analyzer to measure a three-point flexural strength of a bar 5 mm
thick, 5.7 mm wide, and 50 mm long, supported on a two-point span spaced at a distance of 40
mm. The force to break the test part when applied at the center of the 40 mm span can be used to
calculate an estimate of flexural strength. The current embodiment can typically exhibit flexural
strengths between 10 and 20 MPa after 60 minutes, and 15 to 25 MPa and greater after 120
minutes in the build bed after the last layer of the article completed printing. This strength
represents mostly the anaerobic strength development that occurs within the article, while the
aerobic curing occurring within 200 microns from the surface of the article is still ongoing at a
slower rate. The article may exhibit a tacky surface at 60 minutes, but may exhibit a durable and
handle-able strength.
[0088] Figure 14 shows the typical response of aerobic cure when measured using the test
part 1500 shown in Figure 15. No curing occurred when the wall on the test part sagged to the
point that it touched the bottom surface of the test part 5 mm away. Partial cure occurred when
the wall crept and sagged downwards but did not touch the bottom surface of the test part. Full
curing occurred when the wall remained horizontal when extracted from the build bed. From
this test, it was determined that after 4 hours, an article with wall thickness of 0.4 mm and less
would have sufficient duration of aerobic curing to develop enough strength to be extracted from

the build bed. The particulate material and fluid binder formulations listed in Table 17 were
used to conduct this test.

Mechanisms of anaerobic and aerobic reaction of the peroxide initiated material system
[0089] When a fluid binder including monomers and/or oligomers with (meth)acrylate
functional groups, monomers and/or oligomers with allyl functional groups, and an organic
hydroperoxide comes in contact with a transition metal catalyst present in a particulate material
suitable for Three Dimensional Printing the organic hydroperoxide is decomposed to initiate a
free radical polymerization. Two reaction mechanisms can be involved at this point of contact:
anaerobic polymerization and aerobic polymerization.
[0090] Anaerobic polymerization occurs where no oxygen is present in the interior portions
of the three dimensional articles being created, e.g., at depths greater than about 0.2 mm from the
surface of the printed article. Aerobic polymerization occurs at the surface and at a depth into
which oxygen is capable of diffusing.

[0091] A simplified kinetic mechanism for free radical polymerization may be represented
by the following steps:
Radical Generation Initiator→Free Radicals
Initiation Free radical + Monomer→Radical Monomer
Propagation Radical Monomer + Monomer→ Radical Polymer
Termination Radical Polymer + Radical Polymer→Polymer
[0092] Anaerobic radical generation occurs when the hydroperoxide is decomposed by a
transition metal capable of oxidizing and reducing its valence charge, such as cobalt. This is
represented by the following mechanism:
Co+2 + ROOH → Co+3 + RO + OH"
[0093] The oxidized Co+3 ion can then be reduced to Co+2 via
Co+3 + ROOH → Co+2 + ROO + H+
and/or
Co+3 + OH→ Co+2 + OH
[0094] RO, ROO, and OH are radicals species that can react with a monomer or oligomer
species and start polymerization. The RO and OH radicals are more efficient under anaerobic
conditions with (meth)acrylate functional monomers and oligomers. Oxygen may react with
these radical species to form weak radicals, or may be scavenged by free radical inhibitors that
use oxygen to function, such as the most common type of inhibitors based on hydroquinones.
The anaerobic polymerization continues to propagate under anaerobic conditions until
terminated.
[0095] Transition metals like cobalt also assist in the auto-oxidative drying (aerobic curing)
of the allyl ether functional monomers or oligomers by increasing oxygen absorption at the
surface. A radical center is created at the place of allylic hydrogen, where the hydrogen is
abstracted by radicals species from the organic hydroperoxide; or with the assistance of cobalt,
the allylic hydrogen is abstracted by oxygen. The radical center of the allyl group now reacts
further with oxygen to make a peroxide radical. The peroxide radical species can add to double
bonds of (meth)acrylate functional groups or other allyl groups, terminate with other radicals, or
abstract further hydrogen atoms from monomers, oligomers, or the propagating polymer. The

abstraction of hydrogen atoms with and from ally! ethers has a higher probability to propagate
over the termination of peroxy radicals because it can regenerate easily with other abstractable
hydrogens present and is abundant in the formulation based on (meth)acrylate and allyl
functional monomers and oligomers. This aerobic mechanism proceeds at a much slower rate
than the anaerobic mechanism.
[0096] The result of this aerobic mechanism is a highly crosslink polymer network that
forms a non-tacky surface.
[0097] Background information regarding the decomposition mechanisms of hydroperoxides
using cobalt may be found in the Handbook of Adhesive Technology. Pizzi, A. and Mittal, K.L.,
Marcel Dekker, Inc., 2003, and regarding the mechanism of allyllic polymerization in "Polyallyl
Glycidyl Ether Resins for Very Fast Curing High Performance Coatings," presented by
Knapczyk, J. at the 65th Annual Meeting of the Federation of Societies for Coatings Technology,
in Dallas, TX, on October 6, 1987, the disclosures of these references are incorporated herein by
reference in their entireties.
Flow Properties of Build Materials
[0098] Compositions have been disclosed that relate to control of the flow properties of the
build material in Three Dimensional Printers. The three principal methods are the addition of
liquid "processing aids," control of grain size distribution, and the addition of solid fillers that
contribute to the frictional behavior of the build material. Many candidate materials have been
disclosed previously, for example, in U.S. Patent Publication Number 2005/0003189, the
disclosure of which is incorporated herein by reference in its entirety. Some mechanical
properties of dry particulate build materials are disclosed in the following discussion that are
particularly suited for use in Three Dimensional Printing, especially in contrast to other
formulations of similar materials for other uses that do not require special flow characteristics of
the raw materials.

[0100] A method that may be used to quantify a particulate material's suitability .for Three
Dimensional Printing includes placing 1 liter in bulk volume of a particulate material in a metal
cylinder with an inside dimension of 6.1 inches, and inside height of 6.2 inches so that the height
of the powder is between 2.5 to 3.0 inches when the cylinder is capped with a transluscent cover
and laid on its side (i.e., the height of the cylinder is horizontal). The drum is then slowly rolled
with a rotational velocity of 2.5 rotations/min +/- 0.5 rotations/min until the powder reaches an
angle where it avalanches upon itself. The distance that the drum rolled, s, is recorded and the
angle, □, can be determined from Equation 6:

where r would equal the outside radius of the drum. The angle, tj>, is the internal angle of friction
that particulate material has under these particular test conditions at a room temperature between
65 to 75°F. Various particulate materials known to have good and bad spreading characteristics
are compared using this test method, and desirable range of internal angles of friction were
determined. Table 18 summarizes the particulate material compositions that were measured.
Referring to Figure 16, a graphical representation of the results collected is provided.

[0101] Based on the results indicated in Table 18 and illustrated in Figure 16, one can
conclude that powders that have an internal angle of friction greater than 40° and less than 70°
are suitable for Three Dimensional Printing.
[0102] Figures 17a and 17b compare surface finish scans from a VIKING laser
profilometer from Solarius. As one may expect, a particulate material with an internal angle of
friction that is between 40° and 70° (Figure 17a) provides a smoother finish than a particulate
material with an internal angle of friction greater than 70° (Figure 17b) where the powder is too
cohesive to spread an even layer of particulate material, resulting in an article that has very
rough and uneven surface finish. Figure 17c is a CAD drawing of die formed part illustrated in
Figures 17a and 17b.
[0103] Figures 18a and 18b compare surface finish scans from a VIKING laser
profilometer from Solarius. As one may expect, a particulate material with an internal angle of
friction that is between 40° and 70° (Figure 18a) provides a smoother finish than a particulate
material with an internal angle of friction less than 40° (Figure 18b) where the powder is too
flowable and unable to resist the spreading forces causing previous printed layers to be
displaced, resulting in an article that has a rough and uneven surface finish, or even artifacts
missing from the surface of the article because they were displaced. Figure 18c is a CAD
drawing of the formed part illustrated in Figures 18a and 18b.
[0104] This test is a fairly useful technique for identifying relative performance properties
between different candidate materials. The preferred method for evaluating flow properties of
candidate build materials during formal optimization after the initial selection period is to test
samples of the material on a working three dimensional printer. Certain pathological
geometries are known to those experienced in the art, and they can be evaluated either
qualitatively or quantitatively. One particularly useful part for observing stability during
spreading is a flat plate studded with pegs that are oriented downward during the build. During
printing, the earliest layers addressed are a series of disconnected patches that are relatively
free to shift in the build material. After these have been formed, a plate is printed that joins all
of the pegs together in a single object. One can easily examine whether the pegs are uniform
and straight, and one can evaluate the quality of spreading on that basis.
[0105] Those skilled in the art will readily appreciate that all compositions and parameters
listed herein are meant to be exemplary and actual compositions and parameters depend upon
the specific application for which the methods and materials of the present invention are used.

It is, therefore,-to be understood that the foregoing embodiments are presented by way of
example only and that, within the scope of die appended claims and equivalents thereto, the
invention may be practiced otherwise than as specifically described.
[0106] What is claimed is:

1. A powder material system for three dimensional printing comprising:
a substantially dry particulate material comprising:
an insoluble filler,
a soluble filler, and
a transition metal catalyst,
wherein the dry particulate material is suitable for use in three dimensional printing to form an
article comprised of a plurality of layers, the layers including a reaction product of the particulate
material and a non-aqueous fluid that contacts the particulate material during three dimensional
printing.
2. The material system of claim 1, wherein an internal angle of friction of the particulate
material has a value selected from a range of 40° to 70°.
3. The material system of claim 1, wherein a critical surface tension of the particulate
material is greater than 20 dynes/cm.
4. The material system of claim 1, wherein the particulate material comprises about 50% -
90% by weight of the insoluble filler, about 10 - 50% by weight of the soluble filler, and about
0.01 - 0.5 % by weight of the transition metal catalyst.
5. The material system of claim 1, wherein the insoluble filler is selected from the group
consisting of solid glass spheres, hollow glass spheres, solid ceramic spheres, hollow ceramic
spheres, potato starch, tabular alumina, calcium sulfate hemihydrate, calcium sulfate dehydrate,
calcium carbonate, ultra-high molecular weight polyethylene, polyamide, poly-cyclic-olefins,
polyurethane, polypropylene and combinations thereof.
6. The material system of claim 1, wherein the soluble filler is selected from the group
consisting of methyl methacrylate polymers, ethyl methacrylate polymers, butyl methacrylate
polymers, polyvinylbutyral, and combinations thereof.
7. The material system of claim 6, wherein the soluble filler has a molecular weight selected
from a range of 100,000 g/mol to 500,000 g/mol.

8. The material system of claim 1, wherein the transition metal catalyst is selected from the
group consisting of cobalt (II) octoate, cobalt (II) naphthenate, vanadium (II) octoate, manganese
naphthenate and combinations thereof.
9. The material system of claim 1, wherein the particulate material further comprises a
pigment.
10. The material system of claim 9, wherein the particulate material comprises about 0.5 -
5% by weight of the pigment.
11. The material system of claim 9, wherein the pigment is selected from the group
consisting of zinc oxide, zinc sulfide, barium sulfate, titanium dioxide, zirconium silicate, lead
carbonate, and hollow borosilicate glass spheres.
12. The material system of claim 1, wherein the particulate material further comprises a
processing aid.
13. The materials system of claim 12, wherein the particulate material comprises about 0.01
- 2.0 % by weight of the processing aid.
14. The material system of claim 12, wherein the processing aid is selected from the group
consisting of mineral oil, propylene glycol di(caprylate/caprate), petroleum jelly, propylene
glycol, di-isobutyl phthalate, di-isononyl phthalate, polyalkyleneoxide modified
heptamethyltrisiloxanes, polyalkyleneoxide modified polydimethylsiloxanes, secondary alcohol
ethoxylated hydrocarbons, hydrogenated hydrocarbon resins, and combinations thereof.
15. A kit comprising:
a substantially dry particulate material comprising:
an insoluble filler;
a soluble filler; and
a transition metal catalyst, and
a fluid binder comprising:
a (meth)acrylate monomer;
at least one of an allyl ether functional monomer or an allyl ether functional
oligomer; and
organic hydroperoxide.

16. The kit of claim 15, wherein the fluid binder comprises about 40% - 95% by weight of
the (meth)acrylate monomer, about 5 - 25% by weight of the allyl ether functional
monomer/oligomer, and about 0.5 - 5% by weight of the organic hydroperoxide.
17. The kit of claim 15, wherein a contact angle of the fluid binder is less than 25° when in
contact with the particulate material.
18 The kit of claim 15, wherein a 1 mm penetration hardening rate of die substantially dry
particulate material upon application of the fluid binder is selected from a range of 0.01/min to
1.0/min.
19. The kit of claim 15, wherein the fluid binder further comprises a (meth)acrylate oligomer.
20. The kit of claim 19, wherein the fluid binder comprises about 10 - 40% by weight of the
(meth)acrylate oligomer.
21. The kit of claim 15, wherein the fluid binder further comprises a surfactant.
22. The kit of claim 15, wherein the dry particulate material further comprises at least one of
a pigment or a processing aid.
23. A method for forming an article by three-dimensional printing, the method comprising
the steps of:
providing a substantially dry particulate material comprising a plurality of adjacent
particles, the particulate material comprising a transition metal catalyst; and
applying to at least some of the plurality of particles a fluid binder in an amount
sufficient to bond those particles together to define at least a portion of the article, the fluid
binder comprising a (meth)acrylate monomer, a (meth)acrylate oligomer, an organic
hydroperoxide and at least one of an allyl ether functional monomer or an allyl ether functional
oligomer.
24. The method of claim 23, whereb the transition metal catalyst induces decomposition of
the organic hydroperoxide to generate free radicals and the free radicals initiate anaerobic
polymerization of the (meth)acrylate monomer and oligomer, and aerobic polymerization of the
at least one of the allyl ether functional monomer or the allyl ether functional oligomer.
25. The method of claim 23, wherein the particulate material further comprises at least one of
an insoluble filler, a soluble filler, a pigment, or a processing aid.

A materials system and methods are provided to enable the formation of articles by Three
Dimensional Printing. The materials system includes a transition metal catalyst that facilitates the reaction of an acrylate-containing binder with a particulate material.